Drive wheels of commercial trucks and busses are generally driven by transverse axles that connect wheels mounted on wheel hubs to a large differential disposed in the center of the vehicle body. The vehicle body includes a rigid frame that is supported on a spring suspension on the axles. Brakes are generally provided adjacent the wheel hubs.
Some of the disadvantages associated with such designs are loading restrictions and high floor heights that are generally required to maintain vertical clearance between the vehicle body, the differential and other parts of the drive axle assembly. Attempts to minimize these problems have included mounting the differential to the vehicle body and using universal joints in the axles. This approach has required complex wheel support structures that lack durability and add cost.
Prior art bus designs generally have relatively high floors that require at least two steps in the doorway for ingress and egress. To make such buses useable by handicapped persons it is normally necessary to add a wheelchair lift.
Prior art commercial truck designs, especially of the type used for package delivery, normally have rear wheel drive with a front end mounted engine. Problems associated with these trucks include a relatively high floor height, vehicle weight, payload weight and space constraints.
Examples of prior art designs are disclosed in U.S. Pat. No. 4,362,221 and U.S. Pat. No. 4,343,375 that each disclose a vehicle drive wheel suspension in which the differential housing is carried by the body and frame structure of the vehicle while the wheels are connected to the differential by live axles having universal joints. Wheel bearings are connected to rigid support members forming part of the laterally opposite ends of the drive axle. The support members are connected by transversely extending rails that require clearance forward and rearward of the differential for vertical movement.
These and other disadvantages and problems associated with prior art designs are addressed by the invention as summarized below.